The invention relates generally to methods and apparatus for scanning arrays of information-containing locations where the information is embodied in current signals having large dynamic range. More particularly, the invention relates to methods and apparatus for scanning two-dimensional processing surfaces comprised of numerous individual local analog processing elements doing local spatial processing which generate output information in the form of current signals which can vary by as many as 4-5 orders of magnitude in amplitude and which can change sign.
There is an ongoing interest in further development of processing planes comprised of large numbers of local, simple processing elements which do local spatial processing of input information. Such input information can include visible light input, auditory input, or other patterns of signal activity. Further, such processing planes can include neural networks wherein the operation of the brain is emulated. In such processing planes, information in the form of memories and processes such as association can be represented by outputs in the form of current signals having variable sign and large dynamic range.
The advantage of using such processing planes having numerous processing elements is that a great deal of processing may be done in concurrent fashion, thereby allowing large amounts of information to be processed in a short time.
However, the use of processing planes creates certain problems in attempting to utilize the information generated on the processing plane. Typically, all the information generated by all the processing elements on the plane must be periodically read and evaluated or subjected to further processing. Typically, this scanning of the processing elements in the plane occurs periodically at a very high repetition rate. This requires that the information from very large numbers of processing elements, on the order of 104 individual processing units, be read out at sufficiently rapid rates to allow further processing to be performed. Such further processing of the signals from the local processing elements can include such processes as pattern recognition, movement detection and so on. This repetitive readout of the information generated on the processing plane must be done very rapidly to allow very complex and changing input stimulus to be analyzed with sufficient resolution in time. Large numbers of processors are required for adequate resolution in space.
Typically, the output signals from the individual processing elements on the processing plane are very tiny currents which can change in sign and which can vary in amplitude by as many as 10.sup.5 orders of magnitude. Therefore, a need has arisen for a scanning circuit and method which can rapidly scan information off a processing plane having on the order of 10,000 or more processing elements where the information is embodied in the form of currents having amplitudes as small as picoamperes which can change in sign and vary by as many as five orders of magnitude.